MEXICO CITY (AP) — President Donald Trump is offering no evidence to support his assertion that “unknown Middle Easterners are mixed in” with Central American migrants moving toward the U.S. southern border. Associated Press journalists who have traveled with the migrant caravan for more than a week have seen nothing that verifies his claim.

TRUMP: “Sadly, it looks like Mexico’s Police and Military are unable to stop the Caravan heading to the Southern Border of the United States. Criminals and unknown Middle Easterners are mixed in. I have alerted Border Patrol and Military that this is a National Emergy. Must change laws!” — tweet Monday.

THE FACTS: Unless Trump possesses information unknown to the public, his statement appears grounded in nothing more than years-old rumors about Islamic terrorists sneaking into the U.S. from Mexico. No cases of that happening have been recorded.

The migrants participating in this caravan are mostly from Honduras, where it started, as well as El Salvador and Guatemala. On the whole they are poor, carrying the belongings that fit into a knapsack and fleeing gang violence or poverty.

Are some criminals mixed in with the throngs? That’s probably true, given the sheer number of migrants. Trump did not substantiate his claim that members of the MS-13 gang, in particular, are among them.

Some migrants clashed with Mexican police at the Mexico-Guatemala border, hurling stones and other objects as they tried to cross the international bridge. Caravan leaders said they had expelled a number of troublemakers from the procession, exhibiting some self-policing. Ultimately, most entered Guatemala — and later, Mexico — by illegally bypassing immigration checkpoints.

The caravan otherwise has been overwhelmingly peaceful, receiving applause and donated food from residents of the towns they pass. Mexican police have not tried again to stop them.

Guatemalan officials say they detained several Syrian citizens with false documents two years ago and deported them. No evidence was made public connecting them to the Islamic State or this caravan.